How a saber-toothed cat is like a can opener

The enormous canine teeth that make extinct saber-toothed animals so frightening weren’t very practical. Consider the saber-toothed cat Smilodon fatalis. This animal was smaller than a lion but nearly twice as heavy. It probably couldn’t have chased down its prey, instead relying on ambush tactics. And to operate those big chompers, the cat’s head and jaw were shaped differently from modern cats.

“Huge teeth got in the way of more than just running; they made eating and other basic activities difficult,” biologist Douglas Emlen of the University of Montana in Missoula notes in his upcoming book Animal Weapons: The Evolution of Battle. “The simple act of ingesting food was awkward because the enormous canines got in the way.”

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Smilodon first appeared 1.6 million years ago and lived in North America and western South America, but the cats went extinct some 10,000 years ago. With no modern comparable animals, scientists have had to theorize how saber-toothed animals managed to employ those big canines. At first, researchers thought that Smilodon used its teeth like knives — or sabers — to slash and stab its prey, causing enough damage or blood loss to ensure death. But scientists argued that such a motion wouldn’t have had enough force to cut through the thick hide of a prey animal.

Then in 1985, a researcher at the Natural History Museum of Los Angeles proposed that the cat employed its lower jaw in the bite, providing an opposing force against which the downward motion of the top jaw could work.

This “canine shear-bite” has been widely accepted since. But that bite “is mechanistically impossible,” Jeffrey G. Brown, an anatomic and clinical pathologist from New York City, argues October 1 in PLOS ONE . Instead, he says, the cats operated the tops of their skulls (topped with those big teeth) like old-school can openers .

Brown bought a replica of an S. fatalis skeleton cast and created a simple computer simulation of the cat’s neck and skull. In the canine shear-bite model, the skull acts like a class 3 lever, with the fulcrum at the base of the skull, the load placed at the big teeth and the effort (or force) nearer the fulcrum. The cat uses its forearms to hold its prey in place — necessary to prevent struggling that might cause the canines to break — and powers the bite with its neck. But in the computer simulation, the bite just didn’t work and the jaws wouldn’t close.

So Brown proposes that the cat’s head and teeth were more like a class 1 lever, which places the fulcrum at the joint where the lower jaw attaches to the skull and the effort coming from farther down the animal’s spine. Smilodon would have anchored its lower jaw in its prey, then, placing its forearms on the ground, risen up and rotated its upper jaw around to close the bite. It could have killed simply by compressing the neck of its prey and collapsing the carotid arteries or airway.

“The Class 1 Lever Model is mechanically feasible, consistent with current data on S. fatalis anatomy and ecology, and may provide a basis for similar studies on other fossil taxa,” Brown writes, acknowledging that more tests are needed. It will be interesting to see if his idea holds up.